Noble metal-molecular sieve catalysts

Abstract

Exhaust gas catalysts are disclosed. One exhaust gas catalyst comprises a noble metal and a molecular sieve, and has an infrared spectrum having a characteristic absorption peak from 750 cm−1 to 1050 cm−1 in addition to the absorption peaks for the molecular sieve itself. The exhaust gas catalyst also comprises a noble metal and a molecular sieve, having greater than 5 percent of the noble metal amount located inside pores of the molecular sieve. The exhaust gas catalyst also comprises a first and second molecular sieve catalyst. The first molecular sieve catalyst comprises a first noble metal and a first molecular sieve, and the second molecular sieve catalyst comprises a second noble metal and a second molecular sieve. The first and second molecular sieves are different. The invention also includes exhaust systems comprising the exhaust gas catalysts, and a method for treating exhaust gas utilizing the exhaust gas catalysts.

Description

FIELD OF THE INVENTION[0001]The invention relates to exhaust gas catalysts and their use in an exhaust system for internal combustion engines.BACKGROUND OF THE INVENTION[0002]Internal combustion engines produce exhaust gases containing a variety of pollutants, including nitrogen oxides (“NOx”), carbon monoxide, and uncombusted hydrocarbons, which are the subject of governmental legislation. Emission control systems are widely utilized to reduce the amount of these pollutants emitted to atmosphere, and typically achieve very high efficiencies once they reach their operating temperature (typically, 200° C. and higher). However, these systems are relatively inefficient below their operating temperature (the “cold start” period).[0003]For instance, current urea based selective catalytic reduction (SCR) applications implemented for meeting Euro 6b emissions require that the temperature at the urea dosing position be above about 180° C. before urea can be dosed and used to convert NOx. NO...

AI Technical Summary

Problems solved by technology

However, these systems are relatively inefficient below their operating temperature (the “cold start” period).

NOx conversion below 180° C. is difficult to address using the current systems, and future European and US legislation will stress the low temperature NOx storage and conversion.

Currently this is achieved by heating strategies but this has a detrimental effect of CO2 emissions.

As even more stringent national and regional legislation lowers the amount of pollutants that can be emitted from diesel or gasoline engines, reducing emissions during the cold start period is becoming a major challenge.